Fuel injection apparatuses for operating an internal combustion engine have generally been known for many years. With a so-called common rail injection system, fuel is fed into the respective combustion chamber of the internal combustion engine by means of injectors, in particular by means of piezoinjectors. The quality of the combustion is dependent here upon the high-pressure accumulator. The pressure in the high-pressure accumulator must be controlled in order to achieve as high a specific output of the internal combustion engine as possible and at the same time minimal pollutant emissions. In this way, when a high-pressure pump and a pressure accumulator are used for the fuel, injection pressures of 1600 to 1800 bar can be reached.
The pressure in the high-pressure accumulator can be controlled here in different ways. This can take place depending on the design of the injection system using a pressure control valve in the high-pressure region and a volume control valve on the low pressure side of the high pressure pump, or only by means of a volume control valve on the low pressure side of the high pressure pump. The second example, in other words the pressure control with the aid of a volume control valve, is exclusively detailed below. The high pressure accumulator pressure is controlled here by controlling the volume flow in the low pressure region of the high pressure pump. This volume flow control is dependent both on the system requirements, which are determined by the quantity of fuel injected into the combustion chamber, as well as on the fuel quantity which leaves the injectors through the switch leakage losses.
The pressure in the high-pressure accumulator is determined in this case by the fuel quantity supplied by the pump and the fuel quantity escaping via an injection process into the combustion chamber and/or via switch leakages.
The size of an actual pressure gradient value of the high-pressure accumulator is thus dependent on the fuel quantity difference between the fuel quantity, which is delivered from the pump into the high-pressure accumulator, and the fuel quantity which is injected and/or escapes from the injector through switch leakage losses.
If an actual pressure gradient value is now greater than the actual pressure gradient value which is possible for this operating point in the internal combustion engine, this results in a pressure deviation in the high-pressure accumulator, which cannot be counteracted by the pressure controller. A maximum pressure drop and thus a maximum actual pressure gradient value results for instance if the pump no longer conveys fuel into the high pressure accumulator, but at the same time the maximum possible fuel quantity leaves the injector via switch leakages and/or injections into the combustion chamber. If the required target pressure gradient value is now to be greater than the maximum possible actual pressure gradient value, this results for instance in an erroneous increase in the integral part of a PID controller and the control behavior is thus uncalculable.